MET Fusions in NSCLC: Clinicopathologic Features and Response to MET Inhibition

INTRODUCTION

MET fusions have been described only rarely in NSCLC. Thus, data on patient characteristics and treatment response are limited. We here report histopathologic data, patient demographics, and treatment outcome including response to MET tyrosine kinase inhibitor (TKI) therapy in MET fusion-positive NSCLC.

METHODS

Patients with NSCLC and MET fusions were identified mostly by RNA sequencing within the routine molecular screening program of the national Network Genomic Medicine, Germany.

RESULTS

We describe a cohort of nine patients harboring MET fusions. Among these nine patients, two patients had been reported earlier. The overall frequency was 0.29% (95% confidence interval: 0.15-0.55). The tumors were exclusively adenocarcinoma. The cohort was heterogeneous in terms of age, sex, or smoking status. We saw five different fusion partner genes (KIF5B, TRIM4, ST7, PRKAR2B, and CAPZA2) and several different breakpoints. Four patients were treated with a MET TKI leading to two partial responses, one stable disease, and one progressive disease. One patient had a BRAF V600E mutation as acquired resistance mechanism.

CONCLUSIONS

MET fusions are very rare oncogenic driver events in NSCLC and predominantly seem in adenocarcinomas. They are heterogeneous in terms of fusion partners and breakpoints. Patients with MET fusion can benefit from MET TKI therapy.

Resistance to MET inhibition in MET-dependent NSCLC and therapeutic activity after switching from type I to type II MET inhibitors

OBJECTIVES

Resistance to MET inhibition occurs inevitably in MET-dependent non-small cell lung cancer and the underlying mechanisms are insufficiently understood. We describe resistance mechanisms in patients with MET exon 14 skipping mutation (METΔ^ex14), MET amplification, and MET fusion and report treatment outcomes after switching therapy from type I to type II MET inhibitors.

MATERIALS AND METHODS

Pre- and post-treatment biopsies were analysed by NGS (next generation sequencing), digital droplet PCR (polymerase chain reaction), and FISH (fluorescense in situ hybridization). A patient-derived xenograft model was generated in one case.

RESULTS

Of 26 patients with MET tyrosine kinase inhibitor treatment, eight had paired pre- and post-treatment biopsies (Three with MET amplification, three with METΔ^ex14, two with MET fusions (KIF5B-MET and PRKAR2B-MET).) In six patients, mechanisms of resistance were detected, whereas in two cases, the cause of resistance remained unclear. We found off-target resistance mechanisms in four cases with KRAS mutations and HER2 amplifications appearing. Two patients exhibited second-site MET mutations (p.D1246N and p. Y1248H). Three patients received type I and type II MET tyrosine kinase inhibitors sequentially. In two cases, further progressive disease was seen hereafter. The patient with KIF5B-MET fusion received three different MET inhibitors and showed long-lasting stable disease and a repeated response after switching therapy, respectively.

CONCLUSION

Resistance to MET inhibition is heterogeneous with on- and off-target mechanisms occurring regardless of the initial MET aberration. Switching therapy between different types of kinase inhibitors can lead to repeated responses in cases with second-site mutations. Controlled clinical trials in this setting with larger patient numbers are needed, as evidence to date is limited to preclinical data and case series.

CBDCA + Pemetrexed + Bevacizumab and Its Maintenance Chemotherapy in a Case of Solitary Breast Metastasis from a Lung Adenocarcinoma Resistant to Gefitinib

Based on the AVAPERL trial (36th ESMO 2011), CBDCA + pemetrexed + bevacizumab and its maintenance chemotherapy with pemetrexed + bevacizumab is a new promising regimen for the treatment of advanced non-small-cell lung adenocarcinoma. Herein, we report the rare case of a patient with solitary breast metastasis from a lung adenocarcinoma, which was effectively treated using CBDCA + pemetrexed + bevacizumab and its maintenance chemotherapy. A 57-year-old female was admitted to the hospital due to pleural effusion and cardiac tamponade caused by a lung adenocarcinoma possessing a mutation of the epidermal growth factor receptor (EGFR) gene (deletion of exon 19). The patient was treated by first-line chemotherapy (gefitinib 250 mg/body/day) which resulted in complete response. After 12 months, carcinoembryonic antigen was gradually increasing and she complained of a right breast mass. With a core-needle biopsy, the breast tumor was pathologically diagnosed as recurrence and solitary metastasis of a lung adenocarcinoma. Further study of the second mutation of EGFR revealed a T790M mutation. The patient was treated by second-line chemotherapy [CBDCA + pemetrexed + bevacizumab (AUC 6 + 500 mg/m² + 15 mg/kg)] and its maintenance chemotherapy (pemetrexed + bevacizumab). The cases of patients with breast metastasis from other organs are very rare. Immunohistopathological analysis is very useful to diagnose whether the malignancy is primary or not. In the case of a breast tumor with present or previous malignancy, a metastatic breast tumor should be considered. Furthermore, the biopsy of the breast metastasis also revealed the second mutation of resistance to gefitinib, T790M. Of note, according to our case, CBDCA + pemetrexed + bevacizumab and its maintenance chemotherapy is feasible and well tolerated for breast metastasis from a lung adenocarcinoma which is resistant to gefitinib and possesses the T790M mutation in the EGFR gene.